Prepare the Marinade: In a large bowl, whisk together the orange juice, lime juice, olive oil, garlic, cumin, smoked paprika, chili powder, salt, and pepper.
Add the chicken to the marinade, ensuring it is well coated. Cover and refrigerate for at least 30 minutes, or up to 2 hours for more flavor.
Cook the Chicken: Heat a grill pan or skillet over medium-high heat. Remove the chicken from the marinade and cook for 5-6 minutes per side, or until fully cooked and charred in spots. Remove from heat and let it rest for a few minutes before slicing into thin strips.
Prepare the Tacos: Warm the corn tortillas on a dry skillet or directly over a gas flame until lightly charred and pliable.
Assemble the tacos by placing sliced citrus chicken on each tortilla. Top with diced tomatoes, red onion, cotija cheese, and a sprinkle of fresh cilantro.
If desired, add a dollop of sour cream, Greek yogurt, or guacamole on top and serve with lime wedges on the side. Enjoy!